This application claims the priority benefit of Taiwan application serial no. 89122541, filed Oct. 26, 2000.
1. Field of Invention
The present invention relates to a method for stripping a dielectric film. More particularly, the present invention relates to a method for stripping a low dielectric film with a high carbon content from a silicon monitor chip.
2. Description of Related Art
Following the rapid increase in the level of integration and complexity of integrated circuits, the formation of a multiple of metallic interconnect layers is unavoidable. As the number of metallic interconnect layers increases, an overall thickness of deposited layers increases correspondingly. Thickness can be reduced by lowering the dielectric constant of the silicon oxide layer. In general, the lower the dielectric constant, the smaller can be the required thickness of the dielectric layer. Therefore, silicon oxide layer has been largely replaced by a high-carbon-content and low dielectric constant (k) film. Utilizing such high-carbon-content low dielectric film, resistance/capacitance (RC) delay due to line width reduction is minimized. However, the high-carbon-content low dielectric film is formed by using different carbon-containing reactive gases in a plasma-enhanced chemical vapor deposition (PECVD).
Quality of the high-carbon-content low dielectric film in a PECVD process must be closely monitored. Monitoring can be achieved by depositing a low dielectric film over a silicon monitor chip and inspecting the deposited dielectric film thereafter. Since the silicon monitor chip can be reused many times, the dielectric film on the silicon monitor chip is stripped off using hydrofluoric acid solution.
However, the high-carbon-content low dielectric film formed by a plasma-enhanced chemical vapor deposition often contains carbon up to 10%. The carbon atoms inside the dielectric film may react with silicon atoms on the surface of the silicon monitor chip to form carbon-silicon bonds. Once such carbon-silicon bonds are formed, hydrofluoric acid solution can hardly break those bonds and strip the dielectric film from the silicon monitor chip. In addition, the dielectric film is hydrophobic (non-polar) while the stripping agent such as hydrofluoric acid is polar. Hence, wetting capacity of the hydrofluoric acid solution with respect to the dielectric film may be lowered leading to a poor stripping. If the dielectric film is not completely removed from the silicon monitor chip, the monitor chip has to be scrapped or returned for regeneration.
FIG. 1 is a flow chart showing conventional steps of using a silicon monitor chip for inspecting a dielectric films starting from the deposition a dielectric film to stripping the dielectric film and the recycling the silicon monitor chip. In general, a high-carbon-content low dielectric film is formed over a control monitor chip in a plasma-enhanced chemical vapor deposition. Quality of the film deposited on the control monitor chip is later inspected before applying a hydrofluoric acid solution to strip off the dielectric film. However, because the deposited dielectric film is a high-carbon-content material, carbon atoms will react with silicon atoms on the silicon monitor chip to form strong carbon-silicon bonds. The carbon-silicon bonds are particularly hard for hydrofluoric acid to break. Ultimately, only a portion of the dielectric film is removed from the silicon monitor chip. Furthermore, the dielectric film is hydrophobic (non-polar) while the stripping agentxe2x80x94the hydrofluoric acidxe2x80x94is polar. Hence, wetting capacity of the hydrofluoric acid solution with respect to the dielectric film is compromised leading to additional difficulties in stripping off the dielectric film.
Accordingly, one object of the present invention is to provide a method for stripping a high-carbon-content low dielectric film from a silicon monitor chip.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a method for stripping a low dielectric film with a high carbon content from a silicon monitor chip. First, the silicon monitor chip is placed inside a plasma-enhanced chemical vapor deposition chamber and then the surface of the silicon monitor chip is treated with oxygen plasma to form a silicon-rich oxide layer. The silicon-rich oxide layer serves to prevent the formation of bonds between the silicon atoms in the silicon monitor chip and the carbon atoms within the subsequently deposited dielectric film. A high-carbon-content low dielectric film is formed over the silicon-rich oxide for film quality inspection. After the film inspection, the silicon monitor chip is immersed in a solution containing ammonium hydroxide and hydrogen peroxide so that the surface of the dielectric film is transformed from hydrophobic to hydrophilic. Hence, wetting capacity of subsequently applied hydrofluoric acid solution is enhanced. Finally, the silicon monitor chip is immersed in a hydrofluoric acid solution whose concentration is greater than 30% to strip away the low dielectric film.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.